year 8 maths

3J
Time
165
■ The Earth is divided into 24 time zones (one for each hour).
• Twenty-four 15° lines of longitude divide the Earth into its time zones. Time zones also
depend on a country’s borders and its proximity to other countries. (See map on pages
166–7 for details.)
• Time is based on the time in a place called Greenwich, United Kingdom, and this is called
Coordinated Universal Time (UTC) or Greenwich Mean Time (GMT).
• Places east of Greenwich are ahead in time.
• Places west of Greenwich are behind in time.
Key ideas
■ Australia has three time zones:
• Eastern Standard Time (EST), which is UTC plus 10 hours.
• Central Standard Time (CST), which is UTC plus 9.5 hours.
• Western Standard Time (WST), which is UTC plus 8 hours.
Example 20
Converting units of time
Convert these times to the units shown in the brackets.
a 3 days (minutes) b 30 months (years)
SOLUTION
a
b
3 days = 3 × 24 h
= 3 × 24 × 60 min
= 4320 min
30 months = 30 ÷ 12 years
EXPLANATION
1 day = 24 hours
1 hour = 60 minutes
= 2 1 2 years There are 12 months in 1 year.
Example 21
Using 24-hour time
Write these times using the system given in the brackets.
a 4:30 p.m. ( 24 -hour time) b 1945 hours (a.m./p.m.)
SOLUTION
a 4:30 p.m. = 1200 + 0430
= 1630 hours
EXPLANATION
Since the time is p.m., add 12 hours to
0430 hours.
b 1945 hours = 7:45 p.m . Since the time is after 1200 hours, subtract
12 hours.
Cambridge Maths NSW
Stage 4 Year 8 Second edition
ISBN 978-1-108-46627-1 © Palmer et al. 2018
Cambridge University Press
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